Influence of doping on thermal stability of Si/Si1−xGex/Si heterostructures

The thermal stability of Si/Si0.8Ge0.2/Si npn and pnp structures grown by reduced pressure chemical vapor deposition has been studied. The influences of the diffusion of dopants in SiGe or adjacent layers on the thermal stability of the structure are also discussed. The thermal stability of the structures is shown to be dramatically increased compared to that of intrinsic layers when doping the strained Si0.8Ge0.2 layer with boron, phosphorus or arsenic. This performance is attributed to competition between dopant diffusion/precipitation phenomena and misfit dislocation development in the doped SiGe. Moreover, it is observed that doping only the Si buffer and cap layers in the Si/SiGe/Si structure also results in an enhancement in the thermal stability of the SiGe layer. Finally, when pnp or npn structures are grown, the structures exhibit significantly enhanced thermal stability. In addition, the boron out-diffusion from the SiGe layer is retarded in the sample where the Si buffer and cap layers were doped with phosphorus, presumably by in-diffusion of phosphorus into the SiGe layer. In this study, high-resolution X-ray reciprocal lattice mapping and secondary ion mass spectroscopy have been used as the main analysis tools.